Enzymatic bleach compositions comprising a hydrogen peroxide-generating system are well known in the art. For instance, GB-A-2 101 167 (Unilever) discloses an enzymatic hydrogen peroxide-generating system comprising a C.sub.1 -C.sub.4 alkanol oxidase and a C.sub.1 -C.sub.4 alkanol. Such enzymatic bleach compositions may be used in detergent compositions for fabric washing, in which they may effectively provide a low-temperature enzymatic bleach system. In the wash liquor, the alkanol oxidase enzyme catalyses the reaction between dissolved oxygen and the alkanol to form an aldehyde and hydrogen peroxide.
In order to obtain a significant bleach effect at low wash temperatures, e.g. at 15.degree.-55.degree. C., hydrogen peroxide must be activated by means of a bleach activator. Today, the most commonly used bleach activator is tetra-acetyl ethylene diamine (TAED), which yields peracetic acid upon reacting with the hydrogen peroxide, the peracetic acid being the actual bleaching agent.
It is essential in using such bleaching detergent compositions that they are essentially free of catalase activity, because catalase efficiently catalyses the decomposition of the hydrogen peroxide formed by the alkanol oxidase enzyme. Therefore, the alkanol oxidase enzyme must be thoroughly purified in order to liberate it from any contaminating catalase activity. As catalase is abundantly present in all naturally occurring micro-organisms serving as a source for alkanol oxidase, this purification process is essential and it must be carried out extensively, which adds to the cost of the bleaching compositions.
The problem of catalase contamination of the alkanol oxidase may be avoided by isolating the enzyme from a catalase-free micro-organism, such as described for example in EP-A-244 920 (Unilever).
However, even when using catalase-free preparations of the alkanol oxidase enzyme, the bleaching performance of such enzymatic bleach compositions, especially in domestic washing machines of the European type, has not been as good as expected. This has been attributed to the forming of acetaldehyde which is formed in stoichiometric amounts with the hydrogen peroxide. The acetaldehyde is believed to react rapidly with any generated peracid to form acetic acid and the carboxylic acid corresponding to the peracid.
In order to overcome this problem, it has been proposed in EP-A-369 678 (Unilever), to incorporate into such enzymatic bleach compositions, a C.sub.1 -C.sub.4 aldehyde oxidase, the K.sub.m of the aldehyde oxidase being lower than that of the alkanol oxidase. It is believed that the aldehyde oxidase enzyme improves the performance of a detergent composition comprising an alkanol, an alkanol oxidase and a bleach activator by preventing the build-up of inhibiting concentrations of aldehyde. Supportive for this idea is the finding that certain chemical compounds which are known to react with aldehydes--such as semicarbazide--are also capable of improving the performance of the known alkanol oxidase based bleaching compositions.
However, enzymes in general are expensive ingredients of a detergent composition, an aldehyde oxidase is no exception. Furthermore, it has proven to be difficult to find an economically acceptable large-scale production system for aldehyde oxidase.
It is therefore an object of the present invention to provide an effective, low temperature bleach composition. It is another object of the invention to provide a bleach composition comprising an enzymatic hydrogen peroxide-generating system, which has good bleaching properties and does not necessarily contain aldehyde oxidase.
It has now surprisingly been found that an effective enzymatic bleach compositions containing an enzymatic hydrogen peroxide-generating system may be obtained by the bleach composition of the present invention, which are characterized in that they further comprise a bleach catalyst in the form of a manganese (Mn) and/or iron (Fe) ions containing coordination complex.
Bleach catalysts in the form of coordination complexes of manganese (Mn) and/or iron (Fe) ions are known in the art, for instance from EP-A-458 397, EP-A-458 398, EP-A-544 519 and EP-A-549 272 (all Unilever). In combination with hydrogen peroxide, they constitute a strong oxidation system.
Because such manganese and/or iron based coordination complexes form a strong oxidation system in combination with the hydrogen peroxide, the man skilled in the art would have expected that a rapid reaction would occur between the hydrogen peroxide and the aldehyde which is formed by the action of the alkanol oxidase on the alkanol. Surprisingly, however, no such reaction occurs and effective bleaching compositions are obtained.
The compositions of the invention comprising a bleach catalyst in the form of a manganese (Mn) and/or iron (Fe) ions containing coordination complex are especially advantegeous in combination with the enzymatic hydrogen peroxide-generating system, because the latter provides the bleach catalyst with a controllable, steady-state level of hydrogen peroxide such that the bleaching action may be kept within predetermined limits. An additional advantegeous feature of the bleaching compositions of the invention is, that at temperatures well over the recommended washing temperature, for instance at 90.degree. C., the enzymatic hydrogen peroxide-generating system is inactivated and the bleaching action automatically ceases.